Device for generating a beam of ions of high velocity



Aug. 27, 1940. 2,213,140

HARTMUT ISRAEL KALLMANN. FORMERLY KNOWN AS HARTMUT KALLMANN El AL DEVICE FOR GENERATING- A BEAM OF IONS OF HIGH VELOCITY Filed Feb. 10. 1939 Patented Aug. 27, 1940 UNITED STATES DEVICE FOR GENERATING A BEAM OF IONS OF HIGH VELOCITY Hartmut Israel Kallmann, formerly known as Hartmut Kallmann,

Berlin-Charlottenburg,

and Ernst Kuhn, Berlin, Germany, assignors to I. G. Farbenindustrie Aktiengesellschaft Application February 10, 1939, Serial No. 255,755 In Germany February 12, 1938 3 Claims.

It is known that in a vacuum tube positive ions can be neutralised by slight collisions with a gas molecule. This process takes place with only very little loss of kinetic energy. Therefore the formed neutral particles have nearly the same velocity as the positive ions. By a similar process these neutral particles can capture an electron and then form negative ions which again have nearly the same velocity as the aforesaid positive ions. The reversed process may also take place. Negative ions are transformed into neutral particles by losing an electron and those neutral particles then are transformed into positive ions by losing a second electron. This process too goes on with only very little loss of velocity.

Further it is known that ions of high velocity can be generated by multiple acceleration of positive ions in the following way. Positive ions are accelerated by a certain voltage whereafter they are neutralised. Those neutral particles, the velocity of which corresponds to the used accelerating voltage, now pass through the same voltage, however, with the reversed sign. Thereon the neutral particles are again ionised and accelerated another time. By repeating this process several times, positive ions of very high velocity are finally generated. However, the intensity of the beam of positive ions is very much reduced by the repeated transformation of positive ions into neutral particles, as this process is a rather improbable one at high voltages. The gain of this transformation often amounts to about 0.1% only.

The neutralisation of negative ions and the ionisation of the neutral particles, however, are essentially more probable processes at high volt ages. Under favourable circumstances and at sufiiciently high voltages most of the negative ions can be transformed into positive ions. Therefore the device according to the present invention employs negative ions generated by a special ion source created by electron capture of positive ions and neutral particles. These negative ions of low velocity are accelerated by an electrostatic field to negative ions of high Velocity, thereafter in the aforementioned way they are transformed into positive ions without practically any loss of velocity. These positive ions having the same velocity as the accelerated negative ions are likewise accelerated to ions of still higher energy by a similar electrostatic field. It is practical to make the amount of the accelerating voltage of the positive ions just equal to the accelerating voltage of the negative-ions. In this case the voltage used for accelerating the positive ions is the same as that used for accelerating the negative ions, the field in the latter case, however, having the reversed sign. The electrode on which the positive ions impinge thus has thesame potential as the forementioned source of negative ions.

As the source of negative ions and the collecting electrode for the positive ions are of the same potential it is practical to connect them both to ground. Sometimes it also will be practical to ground the walls of the vacuum tube. The positively charged electrode is introduced into the vacuum tube by means of an isulating bushing.

The insulator separating the high potential electrode from the two earthed electrodes must be very large by reason of the very high potentials used. In view thereof it has been suggested to enclose the entire device in a receptacle filled with a compressed gas, but this not only renders the apparatus very bulky, but the device proper is accessible only with great difficulty.

Now, the present invention relates to an essentially improved constructional form in which solely the outer side of the leading-in insulator and those parts of the supply lead of the highpotential electrode which are in contact with the outer air are enclosed in a space filled with compressed gas. The invention is illustrated diagrammatically and by way of example on the accompanying drawing partly (upper half) in side-view and partly (lower half) in vertical section.

The positive ions generated in the source of ions l pass into the channel 2 and are partly transformed therein to negative ions before entering into the discharge space 3. The beam of minus negative ions t is accelerated by the field existing between the outlet aperture 2 and the positively charged high-potential electrode 5. The ions pass through the channel 6 of this electrode into which the gas is continually introduced through the tube l so that the pressure in the channel 6 is higher than in the space 3, as a pump (not shown) connected up to the space 3 by the tube 8 continually evacuates this space.

In the channel 5 of the high-potential electrode 5 the negative ions are transformed to positive ions which then are again accelerated by the electric field existing between the electrode 5 and the collecting electrode 9 so that they impinge with a very high speed upon the substance to be irradiated.

The insulating body H and the outer end of the electrode El are enclosed in a hollow body l2 which is filled with a compressed gas. The outer end of the electrode 5 is preferably formed as a body is witht large radius of curvature for protection against glow or corona discharge within which the device supplying the channel 6 through the pipe 7 with gas may be housed. For charging the high-potential electrode 5 in a well known manner a movable band consisting of an insulating material, for instance a silk-band Hi, may be used, the band being charged at I5 within the space containing the compressed gas.

We claim:

1. A device for generating a beam of ions of high velocity comprising a casing, a source of negative ions, an accelerating electrode functioning to convert the negative ions to positive ions spaced from said ion source and including a perforated portion in the path of said negative ions and a conduit portion for the supply or" gas to the perforated portion, said conduit portion extending outside said casing, a collecting electrode spaced from said accelerating and converting electrode and providing means for accelerating ions transformed in sign by said accelerating and converting electrode, an insulating member separating the outer end of said accelerating and converting electrode from said casing and a second casing adapted to provide a body of high pressure gas about the outer end of said accelerating and converting electrode and the portion of said insulating member adjacent thereto.

2. A device as defined in claim 1 wherein the outer portion of said accelerating and converting electrode forms a body of large radius of curvature whereby corona discharge therefrom is minimized.

3. A device as defined in claim 1 wherein a charging device for bringing said accelerating and converting electrode to a high potentiial is positioned within said body of high pressure gas.

HARTMUT ISRAEL KALLMANN, Formerly known as Hartmut Kallmamt.

ERNST KUHN. 

